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8/13/2019 07 PPP TTE Heat Exchanger Inspection
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Matthews Engineering Training Ltd
INSPECTING HEAT
EXCHANGERS
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INSPECTING HEAT EXCHANGERS
Shell-and-tube type Plate type
We will look mainly at these (most are
statutory equipment as they contain
relevant fluids)
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Some heat exchanger technical standards
TEMA 8thEd :Standards for design and
construction of heat exchangers
API 662 :Plate heat exchanger specifications
API 660 :Shell and tube heat exchangers forgeneral refinery service
ASME PTC 39 : Air cooled heat exchangers
INSPECTING HEAT EXCHANGERS
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The TEMA regulations
(Tubular Equipment Manufacturers
Association
A USA technical standard ( but also used for guidance
in most other countries)
INSPECTING HEAT EXCHANGERS
TEMA is the main design document of interest to
inspectors
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TEMA sections
1.Nomenclature (names of heat exchanger components)
2.Manufacturing tolerances
3.General fabrication information
4.Performance and operation
5.Design information
6.Flowinduced vibration7.Thermodynamics
8.Properties of fluids
9/10: Recommended good practice
Most useful
parts for
inspectors
INSPECTING HEAT EXCHANGERS
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TEMA classes : R, C and B
R: Severe applications : Petrochemical industry
C: Moderate applications:General process uses
B: Chemical process service
High risk
Low risk
R C B = Differences in : Minimum corrosion allowanceTube pitch,shell thickness and other design parameters
INSPECTING HEAT
EXCHANGERS
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TEMA
EXCHANGERS
ARECLASSIFIED
BY TYPE
:USING A 3-
LETTERACRONYM
First letter
:Front end
arrangement
Second letter
:Shell flow path
Third letter
:Back end
arrangement
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Exchanger type AESA E
S
TEMA EXCHANGER TYPES
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Kettle reboiler type AKT
A: Channel and removable cover
K: Reboiler configuration
T:Pull-through floatinghead
TEMA TYPES: ANOTHER
EXAMPLE
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CONTACT TYPE EXCHANGER
9% Cr alloy for
high
temperature
steam
attemporator
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ASME V111 Div 1
TEMA TECHNICAL CRITERIA
TEMA covers
predominantly
the tubesheetand tube
components
The pressure
envelope is more
often covered by
pressure vessel
code e.g ASME VIII-I
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G max
TEMA EXAMPLE:NOZZLE
TOLERANCES
Major cause ofoverstressing of
nozzle welds
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IN-SERVICE INSPECTION OF HEAT
EXCHANGERS
Common corrosion and erosionmechanisms
Failure assessment to pressure
envelope code requirements
Failure assessment to TEMA
requirements
3 major areas of interest
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Water jet cleaning before inspection
Steamcleaning can
cause
distortions
IN-SERVICE INSPECTION
Light
distillate is
sometimesused
BUT
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Corrosionproducts
should be
sampled
BEFOREwater
washing
IN-SERVICE INSPECTION
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IN-SERVICE INSPECTION
Example of scale before water
washing
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IN-SERVICE INSPECTION
In-service checks can be divided into 3 parts
Shell Tube bundle Nozzles and fittings
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SHELL INSPECTION
OVERALL wall
thinning (internal orexternal)
LOCALISED wall
thinning (internal orexternal)
Remember: isolated pi t t ingis
often ignored (according to
API 510)
???
Which is the
mostdangerous?
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SHELL INSPECTION
COMMON MECHANISMSARE:
External CUI
Internal wastage
(impingement/erosion/corrosion)
Creep damage (>400
degC)
SCC in stainless steel
components
Flange face
imperfections (often SCC)
Require a
Code
assessment.
(See
inspection
exercise)
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External CUI
Internal wastage
(impingement/erosion/corrosion)
Creep damage (>400
degC)
SCC in stainless steel
components
Flange face
imperfections (often SCC)
SHELL INSPECTION
SOME EXAMPLES:
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SHELL INSPECTION
MORE FLANGE FACEPROBLEMS:
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TEMA gives limits on RF flange face imperfections
Measurement
in radialdirection
SHELL INSPECTION
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Limits of imperfections in RF flange faces
SHELL INSPECTION
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Tubeplate ligament
erosion/cracking
Leaking tube-to-tubesheetjoints
Tubesheet distortion
Scaling/corrosion of tubes
Cracking/erosion of flow
baffles
TUBE BUNDLE INSPECTION
SOME EXAMPLES:
Some of
these require
a Code
assessment.
(See
inspectionexercise)
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TUBE BUNDLE INSPECTION
Tube pitch may be square or triangular
(different TEMA rules for each)
More difficult to
mechanically clean
outside
Ligament
Erosion
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TUBE BUNDLE INSPECTION
CuNi tubes can suffer from
galvanic corrosion caused by
graphite
Graphite is used as
a mandrel lubricant
during
manufacture of thetube
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TUBE BUNDLE INSPECTION
Some types suffer from intergranular
corrosion
Ti tubes can
suffer fromproblems due to
incomplete
annealing
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TUBE BUNDLE INSPECTION
Expanded (rolled)into tubesheet:some are seam welded
Rules of thumb for inspections
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TUBE BUNDLE INSPECTION
The internal joint is rarely seal welded (poor
access)
Note threaded tie bar
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Tubeplate bore measurement using a 3-point device
TUBE BUNDLE INSPECTION
TUBE BUNDLE INSPECTION
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TUBE BUNDLE INSPECTION
Tube-to-tubesheet joints can suffer crevice
corrosion
TUBE BUNDLE INSPECTION
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TUBE BUNDLE INSPECTION
Common internal pitting
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TUBE BUNDLE INSPECTION
NDT of heat exchanger tubes
1. Borescope (90 head)
2. Eddy current testing
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ECT INSPECTION OF TUBES
ECTcan locate:Wall thinning (loss of material due to
corrosion)
Surface breaking cracks (only)
Principle:
1. A probe induces eddy currents into the
material
2.Cracks or lack of material affects the
response and is measured by an electric
circuit
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ECT INSPECTION OF TUBES
Probe traversed through each tube
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ECT INSPECTION OF TUBES
Note defect categorisation
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FITTINGS:BAFFLE IMPINGEMENT
Maximum clearance (TEMA)
between baffles and shellapprox 5mm
Impingement
wear
Wear is worst around inlet nozzle
area
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INSPECTING HEAT EXCHANGERS
1. Heat exchangers are PRESSURE EQUIPMENT
2. Hundreds of different designs(TEMA categories)
3. Specialised NDT techniques (ECT)
4. Heat exchangers are often (statutory) coded
equipment
5. Corrosion/damage requires an assessment againstcode
KEY POINT SUMMARY
WHAT IS THE RELATIONSHIP BETWEEN
THESE?
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